A conventional communication circuit may use 9 SAW (Surface Acoustic Wave) filters. These SAW filters facilitate split band coverage to avoid interference with a central ISM (Industrial Scientific and Medical, or WiFi) band.
Filters in a conventional communication circuit are unidirectional, and thus either filter transmission (TX) signals or filter reception (RX) signals (but never both).
FIG. 1 illustrates a conventional communication circuit with its major components. Specifically, FIG. 1 illustrates: communication circuitry COMCKT including controller CKT14, transceiver CKT2, diversity filters CKT4, diversity switches CK6, high band pad CKT8, high band filters CKT10, high band switches CKT12, diversity antenna ANTDIV, and main antenna ANTMAIN. Additionally, FIG. 2 illustrates details of transceiver CKT2, diversity filters CKT4, and diversity switches CKT6. FIG. 3 illustrates details of high band pad CKT8, high band filters CKT10, and high band switches CKT12.
Controller CKT14 may control: transceiver CKT2 through control line CL2, diversity filters CKT4 through control line CL4, diversity switches CKT6 through control line CL6, high band pad CKT8 through control line CL8, high band filters CKT10 through control line CL10, and ultrahigh band switches CKT12 through control line CL12. Controller CKT14 may include a processor and a non-transitory memory.
A control line such as CL2 may include (not shown) a voltage supply, a serial data line, parallel data lines, a clock signal, a ground, power amplifier control signals, switch control signals, and may also include return signals such as signal power measurements.
FIGS. 2A and 2B illustrate a conventional transceiver, diversity filters, and diversity switches from FIG. 1. Specifically, FIGS. 2A and 2B illustrate exemplary details of transceiver CKT2, diversity filters CKT4, and diversity switches CKT6 from FIG. 1.
Transceiver CKT2 includes many nodes. The node names indicate what bands are transmitted or received by the specific node. Further, “TX” indicates that a main signal is being transmitted. “DRX” indicates that a diversity signal is being transmitted. “RX” indicates that a main signal is received. Thus, the top node is named “B7 TX,” indicating that a main signal (S2) in band 7 is transmitted. Further, bands such as band 40 may be referred to as “band B40” for emphasis that the number “40” refers to a band. Additionally, a filter may be referred to as filtering “band B40 RX” to emphasize that the signal being filtered is a received signal.
From top to bottom, the nodes may be grouped as follows: transmitting main signals; receiving filtered diversity high band signals from switch SW2 of diversity switches CKT6; receiving filtered diversity low band signals from switch SW4 of diversity switches CKT6; and receiving other main signals. Each of these groups is discussed in sequence below.
Two nodes transmit main signals (S2 and S4): B7 TX transmits S2; and B38/40/41/XGP TX transmits S4.
Eight nodes receive high band diversity signals (S6, S8, S12, S14, S16, S18, and S24) as follows: node B41a DRX receives S6; node B1/4 DRX receives S8; node B40 receives S10; node B34 DRX receives S12; node B39 DRX receives S14, node B3 DRX receives S16; node B2 DRX receives S18; node B7 DDRX receives S24;
Six nodes receive low band diversity signals (S26, S28, S30, S32, S34, and S36) as as follows: node B8/D28a DRX receives S26; node B20 DRX receives signal S28; node B26 DRX receives S30; node B13/B17 receives S32; node B29 DRX receives S34; and node B28b DRX receives S36.
Four nodes receive main band signals (S38, S40, S42, and S44): node B40a/B41a RX receives S38; node B40b RX receives S40; node B38/XGP/B41b RX receives S42; and node B7/41c RX receives S44.
Diversity filters CKT4 include filters F6, F8, F9, F11, F12, F14, F16, F18, F20, F22, F24, F25, F27, F28, F30, F32, F34, and F36.
Diversity switches CKT6 include high band switch SW2 and low band switch SW4 located on a thin SOI (silicon on insulator) die DIE2. High band switch SW2 may be a SP10T (single pole, ten throw) switch. Low band switch SW4 may be a SP7T (single pole, seven throw) switch.
High band switch SW2 receives high band diversity signal S46 at single pole SP2, and transmits high band diversity signal S46 to a selected one of ten throws (T6, T8, T9, T11, T13, T16, T18, T20, T22, and T24), to be transmitted towards diversity filters CKT4 as signals S6, S8, S9, S11, S13, S16, S18, S20, S22, and S24 respectively.
High band switch SW2 may include an additional throw (not shown) for grounding.
Low band switch SW4 receives low band diversity signal S48 at single pole SP4, and transmits low band diversity signal S48 to a selected one of seven throws (T25, T27, T28, T30, T32, T34, and T36), to be transmitted towards diversity filters CKT4 as signals S25, S27, S28, S30, S32, S34, and S36 respectively.
Three filters (F6, F9, and F11) deserve special attention for future reference. Filter F6 receives signal S6 from throw T6, and transmits filtered signal S6 to node B41a DRX in transceiver CKT2.
Filter F9 receives signal S9 from throw T9 and transmits S10 (filtered signal S9) to node B40 DRX. Filter F11 receives signal S11 and transmits signal S10 (filtered signal S11) to node B40 DRX. If switch SW2 is thrown to T9, then node B40 DRX will receive signal S9 filtered through filter F9. Alternatively, if switch SW2 is thrown to T11, then node B40 DRX will receive signal S11 filtered through filter F11. In this fashion, diversity high band signal S46 is filtered by either filter F9 (if T9 is thrown) or filter F11 (if T11 is thrown), and then transmitted as signal S10 to node B40 DRX. Of course, throws T9 and T11 may not be thrown (selected) simultaneously.
FIG. 3 illustrates a conventional high band pad CKT8, high band filters CKT10, and high band switches CKT12 from FIG. 1.
In transmit mode for band 7, high band pad CKT8 receives signal S2 (band 7 being transmitted from node B7 TX), passes this signal through capacitor CAP2 (to filter undesired very low frequency signals), amplifies this signal with amplifier PA2, and sends filtered amplified signal S2 to duplexer DUPB7. Duplexer DUPB7 sends the amplified signal towards main antenna ANTMAIN (not shown) as signal S52 in transmit mode.
Alternatively, in receive mode for band 7, duplexer DUPB7 receives signal S52 from main antenna ANTMAIN, and sends this received signal as S50 towards a transceiver (not shown).
High band pad CKT8 also receives signal S4 (bands 38, 40 and 41 from node B38/40/41), passes this signal through capacitor CAP4 (to filter undesired very low frequency signals), amplifies this signal with amplifier PA4, and sends filtered amplified signal S4 to single pole SP6 of switch SW6.
Switch SW6 is an SP4T (single pole, four throw) having one pole (SP6) and four throws (T54, T56, T58, and T60). If switch SW6 is thrown to throw T54, then filtered amplified signal S4 (band B41 or band B38) is sent to filter F54 in high band filters CKT10. Filter 54 sends filtered signal S54 to high band switches CKT12, specifically to node TX B41b and to throw T54 in switch SW8.
Similarly, throw T56 sends signal S56 (bands B40a and B41) to filters F55 and F57. Filter 55 sends signal S55 (band 40a) to high band switches CKT12. Filter 57 sends signal S57 (band 41a).
Throw T48 sends signal S58 (band B41c) to filter F58. Filter F58 sends filtered signal S58 to high band switches CKT12. Throw T60 sends signal S60 to filter F60. Filter F60 sends filtered signal S60 to high band switches CKT12.
High band filters CKT10 includes 9 filters: transmission filters (F54, F55, F57, F58, and F60), and reception filters (F37, F39, F63, and F65). In TDD operation, one of the transmission filters is being used, or alternatively one of the reception filters is being used. Filter F60 is a low pass filter, and the other filters shown in CKT10 are band pass filters.
High band switches CKT12 include two switches: SP6T (single pole, six throw) switch SW8 (including single pole SP8 and throws T62, T60, T54, T55, T57, and T58), and SP3T (single pole, triple throw) switch SW10 (including single pole SP10 and throws T37, T39, and T64). Switch SW8 and switch SW10 may be placed on a single die DIE4. Die DIE4 may be constructed of MEMS (microelectromechanical systems) or may be solid state SOI (silicon on insulator).
Briefly referring back to FIG. 2, diversity filters CKT4 include filters F6 (band B41a DRX), F9 (band B40 DRX), and FIG. 11 (also band 40 DRX). These filters filter a signal received from the diversity or MIMO (Multiple Input Multiple Output) antenna ANTDIV. These bands are also received through the main antenna ANTMAIN, and filtered by high band filters CKT10.
Switch SW8 is a transmission switch, and transmits signal TX RF1 to main antenna ANTMAIN (not shown). For example, switch SW8 selects throw T55 to transmit band B40a TX through single pole SP8 towards main antenna ANTMAIN (not shown) as signal TX RF1.
In contrast, switch SW10 is a reception switch, and receives signal RX RF1 at single pole SP10 from main antenna ANTMAIN (not shown). For example, switch SW10 selects throw T37, then receives RX RF1 at single pole SP10 and transmits signal S37 (band B40a RX) towards filter F37 in diversity switches CKT10 in route to transceiver CKT2.
TDD (Time-Division Duplex) alternately sends and then receives signals in a given frequency band. In this fashion, band B40a may be alternately sent, and then received over main antenna ANTMAIN (not shown) through switch selections as discussed above. Similarly, band B41a may be time-division duplexed using different switch settings.
Conventionally, as shown in FIGS. 2 and 3, different filters are used for receiving and for transmitting in each band. This conventional approach requires large numbers of filters. For example, high band filters CKT10 illustrates nine filters, and these nine filters are conventionally SAW (surface acoustic wave) or BAW (bulk acoustic wave) filters.
FIG. 4 illustrates a conventional single filter used for transmission and reception of a single band. Specifically, filter F114 is used (alternately, under TDD (Time-Division Duplex) procedures) for filtering a band 38 signal for transmission, and then for filtering a received band 38 signal. Filter F114 is a “dual mode” filter because it filters the transmitted band 38 signal (in a first mode, see FIG. 5C) and also filters the received band 38 signal (in a second mode, see FIG. 5D).
Conventionally (in FIGS. 1, 2, and 3), different filters are used for transmitting and for receiving because transmitted signals are high power (typically 25 dBm, with high insertion loss filters), whereas received signals are low power (typically 0 dBm, with low insertion loss filters). Thus, filters that are dedicated to received signals may use very little power during filtering. In contrast, dual purpose filters (reception or transmission) must be relatively large, and will consume relatively large amounts of power even when filtering received low power signals.
However, there are some advantages to using a single dual purpose (or dual mode, or TX/RX) filter during LTE-TDD communications, such as reducing the number of filters, as shown in FIG. 4.
Filtering circuit CKT14 includes controller CONT4 controlled by control lines CL14, capacitor CAP6, amplifier PA6, switch SW14, switch SW12, filters (F114, F112, and F116), switch SW16, and capacitor CAP8.
Controller CONT4 may be controlled by control lines CL14 that may include a bias voltage, a battery voltage, a clock signal, serial or parallel data signals, and enable signals.
From left to right, signal S100 includes a band 7 transmission signal or a band 38 transmission signal, is filtered by capacitor CAP6, amplified by amplifier PA6, received by single pole SP110 of switch SW14, then switched to throw T112 for the case of a band 7 transmission signal (or switched to throw T114 for the case of a band 38 transmission signal).
FIGS. 5A-5D illustrate the use of a single filter (F114) for transmitting and receiving in band 38 for LTE-TDD communications. Filter F114 is a “dual mode” filter because it filters the transmitted band 38 signal (in a first mode, see FIG. 5C) and also filters the received band 38 signal (in a second mode, see FIG. 5D).
FIG. 5A illustrates the switches and filtering of circuit CKT14 in FIG. 4 for the case of transmitting band 7 (while omitting capacitors, amplifiers, and the controller for the sake of clarity). As discussed above, switch SW14 throws the signal S100 to throw 112. This signal proceeds as signal S102 to filter F112, is filtered, then proceeds as signal S106 to throw T126 of switch SW16.
Signal S106 proceeds from throw T126 to single pole SP120, then exits as signal S110 towards main antennal ANTMAIN.
FIG. 5B illustrates the switches and filtering for the case of receiving band 7 (omitting capacitors, amplifiers, and the controller for the sake of clarity).
A band 7 signal is received by the main antenna ANTMAIN as S110 (or B7 RX), and is sent to single pole SP120 of switch SW16. Single pole SP120 throws the signal to throw T126, and the signal exits as S106 towards filter F116. Filter F116 filters the signal and sends the filtered signal as S114 (B7 RX) towards another location, such as towards a transceiver (not shown). Filter F116 may include a balun (not shown), and may output the received and filtered band 7 signal S114 as differential signals (a positive signal and a negative signal, not shown).
The position of switch SW14 is not shown in FIG. 5B. Power amplifier PA6 may be turned off when receiving the band 7 signal, or switch SW14 may be thrown to throw T114, or switch SW14 may be thrown to a ground (not shown). In other words, generally circuit CKT14 would not simultaneously transmit and receive in band 7, or else the high power transmission band 7 signal would tend to interfere with the relatively low power received band 7 signal.
FIG. 5C illustrates the switches and filtering for the case of transmitting band 38 (omitting capacitors, amplifiers, and the controller for the sake of clarity). Band 38 will be transmitted and received through the same filter F114 (transmitted in FIG. 5C, and received in FIG. 5D).
Switch SW14 throws signal S100 (B38 TX) from single pole SP110 to throw T114. Throw T114 send signal S104 to filter F114. Filter F114 sends filtered signal S108 to throw T124 of switch SW16, then to single pole SP120 of switch SW16. Single pole SP120 sends band 38 signal S110 to main antenna ANTMAIN for transmission.
FIG. 5D illustrates receiving band 38 through filter F114 (previously used for transmitting in the same band 38 in FIG. 5C). FIG. 5D is based on FIG. 4, but omits capacitors, amplifiers, and the controller for the sake of clarity). Thus, FIGS. 5C and 5D illustrate single filter F114 being used for transmitting and receiving the same band 38 in TDD.
In FIG. 5D, a band 38 signal S110 is received by main antenna ANTMAIN and sent to single pole SP120 of switch SW16. Switch SW16 throws the signal to throw T124, then throw T124 sends signal S108 to filter F114. As discussed above, filter F114 now acts as a receiving filter in band 38, instead of as a transmitting filter in band 38. Switch SW12 receives filtered signal S104 at throw T114, and throws this signal to single pole SP120. Single pole SP120 sends received and filtered band 38 signal S112 upwards, possibly to a transceiver. Note that throw T114 of switch SW12 also serves as throw T114 of switch SW14.
Received and filtered band 38 signal S112 may be transformed by a balun (not shown) into differential signals (a positive signal and a negative signal, not shown).
Thus, single filter F114 may alternately serve as a transmission filter (in FIG. 5C) and as a reception filter (in FIG. 5D) during time-division duplexing (TDD) in band 38.
FIG. 6 illustrates using single filters (to transmit and receive) for multiple LTE bands. In FIG. 6, filters F210 and F212 may each be used for filtering in a transmit mode (first mode) and then in a receive mode (second mode), similar to filter F114 discussed above in FIGS. 4, 5C, and 5D.
Specifically, circuit CKT16 includes amplifier circuit CKT18, SP2T (single pole, double throw) switches SW20 and SW22, and filters F210 and F212. Solid signal lines indicate the paths of transmission signals, and dashed lines indicate the paths of reception signals.
Starting at the top left, signal S210 is a transmission signal for bands B38, B40, B41, and XGP. This signal is amplified by amplifier PA10 and sent as signal S212 to switch SW20. Switch SW20 throws this signal to filter F210 as signal S214. Filter F210 transmits filtered signal S216 towards an antenna (not shown. Filter F210 may also filter reception signals (dashed lines) in these bands.
Starting at the top right, filter F210 may receive a signal (dashed line, S218) from the antenna, and filter the signal and pass it to switch SW20. Switch SW20 throws this filtered signal to the lower left pole, and this signal passes to the left and down as signal S218. Thus, switch SW20 will be in a first position when transmitting, and in a second position when receiving signals in bands B38 or B41 or XGP.
Similarly, switch SW22 and filter F212 may filter and transmit a signal in band B40, or may receive and filter a signal in band B40 (depending upon the position of switch SW22.
When transmitting a band B40 signal S220, amplifier PA8 amplifies the signal, filter F214 filters the signal and sends filtered signal S222 to switch SW22, switch SW22 throws the signal to filter F212 as signal S224, then filter F212 filters the signal and sends signal S226 towards an antenna (not shown, and not necessarily the same antenna that signal S216 was sent to).
Starting at the bottom right, filter F212 may receive and filter a band 40 signal (dashed line S228)), then send the filtered signal to switch SW22. Switch SW22 throws this signal to the left and downward as S228.
The received signals S218 and S228 may be transformed into differential signals by baluns (not shown).
Thus, conventional communication circuitry requires too many filters. These numerous filters consume power and take up valuable space.